why is Ralph elected Chief? why did jack fail to kill the piglet ?

1)Ralph has a calm personality that invites the others' trust, so he is elected chief.

2) Jack draws his knife but pauses before he has a chance to stab the pig, which frees itself and runs away. Jack insists that he was merely looking for the right spot on the pig on which to stab it, but his white face suggests that he is unaccustomed to such violence. But he vows that next time, he will show no mercy toward his prey.